1. Field of the Invention
The invention relates to the field of small temperature-sensitive devices, and in particular, to temperature control for small disk drives.
2. Background Information
Small, temperature-sensitive electronic and electromechanical devices, such as micro disk drives, are being developed and used. However, many potential applications for these devices, such as in automotive vehicles, are presently ruled out because of a mismatch between device operating temperature specifications/limitations and automotive operating temperatures. This is true at both the low temperature end and high temperature end of the respective operating temperatures. Besides vehicles, the temperature environment for the emerging market of wearable computers may also be outside of the normal specifications for such devices under certain circumstances.
Existing temperature control methods and adaptations are generally inadequate and/or have drawbacks which make them inapplicable to such devices in these environments. Therefore, there is a need for better temperature control methods and apparatus to adapt these temperature-sensitive devices to be used in a wider variety of operating environments having a wider range of temperatures, such as may be found in the automotive and wearable computer environments.
The present invention is directed to solving the problem of improving temperature control for small, temperature-sensitive devices. In particular, the present invention has been developed to control the temperature environment of xe2x80x98microdrives,xe2x80x99 such as those manufactured by IBM (IBM is a registered trademark of International Business Machines). Microdrives, as the term is used herein, are direct access storage devices (DASD""s) in miniaturized form, e.g., packaged in a relatively small, thin housing, for example, having a thickness of approximately 5 mm or less, and outer dimensions of under 50 mm. In other words, about the size of a small match-box. It should be clear that the inherent small size and low power consumption that a microdrive can provide would clearly be advantageous in situations where these are at a premium, such as in a hand-held device, a wearable computer, or a vehicle.
However, one of the current unresolved issues with using a microdrive in an automotive setting is the mismatch between the automotive operating temperature specifications and those of the microdrive. Disadvantageous external cooling and/or heating apparatus may be required thereby destroying the size and power advantages the microdrive would otherwise provide. To date there have been no solutions proposed that are built into the microdrive. In order to gain rapid acceptance of the microdrive in automotive environments (and other stressed environments), it would be advantageous for the microdrive be a complete OEM entity, that is, having adequate temperature controls already built in.
As with regular-sized DASD""s, microdrives have one or more storage disks which are rotated by a motor and one or more read/write heads. When xe2x80x98loaded,xe2x80x99 that is, positioned for operation with respect to the storage disks over data storage areas, the read/write heads operate to read and write data to and from the storage disks. When not loaded, the heads are xe2x80x98parked,xe2x80x99 that is, positioned at an area off the disk surfaces sometimes called a xe2x80x98load/unload rampxe2x80x99, which is typically located adjacent to the outer edge of the disks in the disk drive.
In practice, based on tests, a microdrive motor can be started and spun without the heads loaded at a temperature as low as xe2x88x9230 C. After the drive reaches a temperature of 5 degrees C. (the lower operating temperature specification), the heads can be loaded and the drive is ready for use. Therefore, some means to warm the microdrive may be required in certain environments.
On the other hand, a microdrive disposed inside of an automobile, for example, might reach a high temperature of 75 degrees C. (non-operating). However, the upper operating temperature of a typical microdrive is around 55 degrees C. Therefore, some means to cool the microdrive down to its operating temperature range is required.
Solid state heating/cooling devices, for example the Peltier thermoelectric module, are known. These modules produce a temperature differential between two surfaces. The effect was discovered in 1834 by Peltier. When a current passes through the junction of two different conductors, it results in a temperature change. The Peltier effect is a thermocouple in reverse. Instead of producing a voltage proportional to temperature, a voltage is used to produce a temperature difference between the two metals in a thermocouple junction. In order to optimize the effect, Peltier devices today use semiconductors such as bismuth telluride. The devices that are commercially available are a sandwich structure as small as 2 millimeters (mm) square and 1 mm thick. Which of the plates is hot and which is cold depends ONLY on the direction of DC current flow.
It is, therefore, a principle object of this invention to provide a method and apparatus for controlling the internal temperature of a small device.
It is another object of the invention to provide a method and apparatus that solves the above mentioned problems so that small, temperature-sensitive devices can be used in a wider range of environments and applications.
These and other objects of the present invention are accomplished by the method and apparatus disclosed herein.
According to an aspect of the invention, an environmental shell is provided that operates in either a heating or cooling mode.
According to another aspect of the invention, heat transfer, either to or from the drive, is aided by the rotating disk or disks inside of the drive. By using the rotating disks as a means to circulate air, one of the limitations of solid state heating/cooling devices, such as a Peltier thermoelectric module, is advantageously overcome, since such devices require a fan or other air circulation mechanism.
According to another aspect of the invention a specially designed cover plate for a microdrive that incorporates a thermoelectric module is provided.
According to another aspect of the invention, a Peltier thermoelectric module is used. The thermoelectric module produces a temperature differential between two surfaces when a current passes through the junction of two different conductors, resulting in a temperature change. This effect was discovered in 1834 by Peltier.
According to another aspect of the invention, the thermoelectric module uses semiconductors such as bismuth telluride. Further, the module is a sandwich structure which may be as small as 2 millimeters (mm) square and 1 mm thick.
According to another aspect of the invention, the thermoelectric module has plates and which of the plates is hot/heated and which is cold/cooled depends only on the direction of direct current flow (DC).
According to another aspect of the invention, the thermoelectric module is integrated into the cover of a microdrive, so that the interior of the microdrive can either be heated or cooled.
According to another aspect of the invention, when cooling the interior, the outside of the microdrive is more efficiently cooled by providing a separate fan combined with fins on the drive.
According to another aspect of the invention, the thermoelectric cooling module can be placed either inside of the microdrive casting or on the outside. In a preferred embodiment, the cooling module is outside of the casting and attached to the top cover of the microdrive. In another preferred embodiment, the thermoelectric cooling unit may be provided with fins and integrated with the top cover of the microdrive.
According another aspect of the invention, miniature thermoelectric modules are used, having dimensions compatible with the size of the microdrive, and which are easily capable of providing over 10 watts of heating power. Since the mass of a typical microdrive is about 16 grams, the required heating or cooling energy required to bring the microdrive to within correct operating specifications within a reasonable time is less than 10 watts. For example, the thermoelectric unit power requirements are 8.8 watts for 60 seconds. A thermoelectric module that fits this requirement is available with outside dimensions of 12.1xc3x9713.2xc3x972.2 mm.
According to another aspect of the invention, the spinning disk(s) in the microdrive are used to assist in heat transfer.
According to an aspect of the invention, the temperature of the microdrive is monitored. If, for example, the microdrive is below xe2x88x9230 degrees C., the thermoelectric module is energized so that the surface closest to the cover of the microdrive, i.e. opposite to the fins, is heated. Heating proceeds with the spindle motor stopped until the drive temperature reaches at least xe2x88x9230 degrees C. At this time, the spindle motor starts while heating continues. After the drive reaches a temperature of 5 degrees C., i.e., the lower temperature specification of the microdrive, the heads can be loaded and the drive is ready for use. The spinning disks entrain air, especially between the inside of the top cover and the surface of the top disk. This provides faster and more even heating of the drive. Similarly, if a drive is too hot, the thermoelectric module is operated with the DC current flowing in the opposite direction, causing the drive cover to become cooler than ambient temperature. The spinning disks aid in the heat transfer process, increasing heat transfer by about ten times based on a rule of thumb for forced convection.
An advantage of this invention is that uses existing technology, i.e., thermoelectric modules, to solve a new problem, i.e., controlling the operating temperature of a microdrive, in a new way. The invention could be used by manufacturers of various small devices besides the small disk drive devices (microdrives) manufactured by IBM.
These and other aspects of the invention will become apparent from the detailed description set forth below.